1. Technical Field
The present invention generally relates to a control apparatus for phase switching of a direct-current (DC) motor and, more particularly, to a control apparatus and a method thereof, capable of counting a count value associated the change of the state of each of the magnetic pole positions of the rotor in the DC motor to adjust each of the PWM signals issued in a next cycle to control the ON or Off states of semiconductor switching devices to lower the vibration noise and increase the rotational speed of the motor.
2. Description of Related Art
Generally, in a conventional DC motor, semiconductor switching devices are often used to implement electronic phase-switching. For example, phase-switching operations are performed by switching the semiconductor switching devices according to detected magnetic pole positions (N poles and S poles) of a rotor in the DC motor. However, during the switching process of the semiconductor switching devices, an unstable coil current may easily occur to induce vibration noise due to motor resonance, which affects the rotational speed of the DC motor. Accordingly, it is important to provide a control circuit and a method thereof, capable of stabilizing the operation of a DC motor.
Substantially, with reference to FIG. 1A, FIG. 1A is a schematic diagram of a driving circuit of a conventional DC motor. The driving circuit 10 is an H-bridge circuit including four semiconductor switching devices Q1˜Q4 and is electrically connected to the DC motor 12 through the output terminals A and B. In addition, during the switching process, the semiconductor switching devices Q1˜Q4 are categorized into two different conducting phases. The semiconductor switching devices Q1 and Q4 are turned on in the first phase, while the semiconductor switching devices Q2 and Q3 are turned on in the second phase. Therefore, the driving circuit 10 has to be controlled to switch between the two conducting phases to effectively drive the DC motor 12 to rotate. Furthermore, referring to FIG. 1B, FIG. 1B is a schematic diagram of a control circuit of a conventional DC motor. An external Hall device HAL is used to sense the change of the state of each of the magnetic pole positions of the rotor in the DC motor 12 to generate a periodic phase-switching signal HC. Then, a control circuit 14 receives a PWM signals PW generated by an external PWM signal generator 16 and the phase-switching signal HC to output switch control signals H1, H2, L1 and L2 to control the ON or Off states of semiconductor switching devices Q1˜Q4 in the driving circuit 10. Afterwards, the driving circuit 10 alternately outputs a first output signal VOUT1 and a second output signal VOUT2 to the DC motor 12 so that the state of each of the magnetic pole positions of the rotor in the DC motor 12 changes accordingly to effectively drive the DC motor 12 to rotate.
However, since the rotor in the DC motor 12 is usually made of permanent magnets, the size of each of the magnetic pole positions of the rotor may vary.